In LTE (Long Term Evolution) and successor systems of LTE (referred to as, for example, “LTE-advanced,” “FRA (Future Radio Access)” and “4G”), a radio communication system (referred to as, for example, “HetNet” (Heterogeneous Network)), in which small cells (including pico cells, femto cells and so on) having relatively small coverages of a radius of approximately several meters to several tens of meters are placed in a macro cell having a relatively large coverage of a radius of approximately several hundred meters to several kilometers, is under study (see, for example, non-patent literature 1).
For this radio communication system, a scenario to use the same frequency band in both the macro cell and the small cells (also referred to as, for example, “co-channel”) and a scenario to use different frequency bands between the macro cell and the small cells (also referred to as, for example, “separate frequencies”) are under study. The latter scenario is under study to use a relatively low frequency band (for example, 0.8 GHz or 2 GHz) in the macro cell and use a relatively high frequency band (for example, 3.5 GHz or 10 GHz) in the small cells.
Also, the system band of the LTE-A system (Rel. 10/11) includes at least one component carrier (CC), where the system band of the LTE system constitutes one unit. Gathering and grouping a plurality of component carriers (cells) into a wide band is referred to as “carrier aggregation” (CA).
Furthermore, in the LTE-A system, coordinated multi-point (CoMP) transmission/reception techniques are under study as techniques to realize inter-cell orthogonalization. In this CoMP transmission/reception, a plurality of cells coordinate and perform the process for transmitting and receiving signals, for one user terminal UE or for a plurality of user terminals UE. For example, on the downlink, simultaneous transmission by multiple cells employing precoding, coordinated scheduling/beamforming and so on are under study. By employing these CoMP transmission/reception techniques, improvement of throughput performance is expected, especially with respect to user terminals UE located on cell edges.